US Defense Secretary James Mattis has said that he has signed deployment orders to send more troops to Afghanistan, days after President Donald Trump announced a new strategy to prolong war in the strategically important country located within South Asia and Central Asia.

“Yes, I’ve signed orders, but it’s not complete. In other words, I’ve signed some of the [orders for] troops that will go and we are identifying the specific ones,” Mattis told reporters at the Pentagon on Thursday.

The Pentagon chief did not say how many troops would be dispatched as part of the deployment orders.

“By and large this is to enable the Afghan forces to fight more effectively. It's more advisers, it's more enablers. Fire support, for example, and there's some other things,” Mattis said.

US Defense Secretary James Mattis

Mattis said the additional troops, which could reportedly approach 4,000, were not on the way to Kabul yet.

"I just signed the order, it's going to take a couple days," he said.

On Wednesday, the US military officially acknowledged there are nearly 3,000 more troops to Afghanistan than the 8,400 previously reported. The additional forces would join the 11,000 troops already in the country.

On August 21, Trump announced his new Afghanistan policy and said he would raise the number of US forces in Afghanistan, citing fight against the Taliban and other terrorist groups. Before his election, Trump had on several occasions voiced his frustration with the 16-year war.

In an executive order issued back in February, Trump tasked Mattis with devising an Afghan strategy that was expected to be delivered in mid-July, but the timeline has reportedly been thrown off by the president’s demand for revisions.

The US-led occupying force officially announced to end its combat operations against the Taliban in the country at the end of 2014, and its current mission is to “train, advise, and assist” Afghan troops.

But General Raymond Thomas, commander of the US Special Operations Command, has said that the new Trump administration would permit more direct engagement between US forces and the Taliban.

The United States -- under Republican George W. Bush’s presidency -- and its allies invaded Afghanistan on October 7, 2001 as part of Washington’s so-called war on terror. The offensive removed the Taliban regime from power, but after more than one and-a-half-decade, the foreign troops are still deployed to the country.

After becoming the president in 2008, President Barack Obama, a Democrat, vowed to end the Afghan war -- one of the longest conflicts in US history – but he failed to keep his promise.

Trump, who has spoken against the Afghan war, has dubbed the 2001 invasion and following occupation of Afghanistan as "Obama's war".